1. Field of the Invention
This invention relates to the improved process for hydrogenation of chloronitrobenzene and fluoronitrobenzene compounds which have acid functionalities, i.e., substituents, and more particularly, to a method whereby dehalogenation of the halonitrobenzene compound can be eliminated during hydrogenation by conducting the reaction in the presence of an acidic catalytic medium.
2. Description of the Prior Art
Catalytic hydrogenation of halogenated nitrobenzene compounds, and the tendency for such compounds to dehalogenate during the process, have been widely reported. Many patents, for example, describe processes for producing halogenated benzenoid amines by catalyzed hydrogenation of the corresponding halogenated benzenoid nitro compounds. Dehalogenation of the benzenoid nucleus, however, usually occurs concurrently with hydrogenation, i.e., reduction of the nitro group, which in turn, may often result in the formation of undesirable by-products. A variety of additives have been used in conjunction with catalysts in an attempt to inhibit and/or minimize dehalogenation. U.S. Pat. No. 3,929,891 discloses a process whereby dehalogenation is limited to less than 0.2% by sulfitizing the platinum catalyst in an acidic suspension previously saturated with hydrogen. The benzenoid nitro compounds which are hydrogenated by the process do not have acidic substituents and this is an essential characteristic of the compounds used in this process. BE 769-220 discloses the preparation of 3-difluorochloromethyl aniline by Group VIII precious metal or metal oxide catalyzed hydrogenation of 3-nitro-difluorochloromethyl benzene. The reaction is conducted in a water miscible solvent in the presence of at least one mole of HCl. The function of the acid is to increase yield and is not to inhibit dehalogenation. Netherlands Patent Publication No. 7311-193 discloses the hydrogenation of nitrobenzenes having substituent halogen, haloalkyl or aliphatic sulfonyl groups using Raney Nickel as the catalyst. The reaction is conducted in an aqueous buffered medium maintaining the pH between 6-7.5 in order to minimize dehalogenation.